Hi akki.cs,
What is the message which comes up?? If the message is 'SAPOSCOL not running ? (shared memory not available )', then this message is probaly coming because you are trying to kill a process which is not started at all.
Try and start the process through ST06 and check whether it starts up.you can do the same through the OS level also.Cliking on the 'Log File' button in ST06 will lead futher details and analysis.

I believe saposcol as a service is required by SAP R/3 for the system to
be up and accessible to users. Having it not initialized or not started
would actually make it impossible for you to run ST06 since SAP itself is
down if that is the case. Do check services.msc on the OS level whether
the service is really down. If error entails "shared memory not available
or initialized" then perhaps your database is down. Can you access SAP MMC
via OS level? Then try restarting the server's R/3 services - but be sure
that if thsi is done in a PRD system, all required steps and notification
to your users are done. Thanks.

I also had a problem with a SAPOSCOL service not starting on one of my APP servers. The problem was the service was trying to make a call back to the CI instead of starting on the actual APP server. You need go to the services on the OS and check the path where it is trying to call the service (start/run/services.msc/SAPOSCOL/Properties/Path to executable). It should be something like this /usr/sap/XXX/D01/exe/SAPOSCOL. Just make sure that it is pointing to the EXE on the local box and not trying to grab it from the CI or anywhere else. If you need to change the path you need to do so in the registry.